1. Technical Field
The present invention relates to an abnormality detection device for a hydraulic circuit and an abnormality detection method for the hydraulic circuit.
2. Related Art
In a hydraulic circuit for a vehicle automatic transmission (for example, CVT (Continuously Variable Transmission), a pressure of oil discharged from an oil pump driven by the power of an engine is regulated, and the regulated oil is supplied. In recent years, the load of the oil pump is required to be reduced for satisfying the request of improving the fuel consumption of the vehicle. As a technique for reducing the load of the oil pump, for example, there is a technique of the oil pump having two discharge ports, which performs switching between a fully discharged state in which oil is discharged from two discharge ports and a partially discharged state in which oil is discharged from one discharge port. As a unit of switching the discharge state, for example, a spool valve and a solenoid valve which moves the spool valve are used.
However, in the case where the discharge state of the oil pump is fixed to the partially discharged state and it is difficult to switch the state to the fully discharged state, there is a danger that an oil discharge amount is short and proper change gear control is inhibited. In order to detect the fixation of the partially discharged state, for example, there is disclosed in Japanese Unexamined Patent Application Publication (JP-A) No. 2013-96540 that it is determined that the oil pump is fixed in the partial capacity operation state (partially discharged state) in the case where an actual gear ratio is lower than a threshold for determining the fixation when the stop of the vehicle is determined.
In the method of determining the fixation disclosed in JP-A No. 2013-96540, it is assumed that the oil pump is fixed in the partially discharged state when the gear ratio is not fully returned to “low” while the vehicle is stopped. However, the state where the gear ratio is not fully returned to “low” while the vehicle is stopped may be caused by other factors such as an abnormality in the automatic transmission besides the fixation of the oil pump. Accordingly, the fixation of the oil pump may be wrongly determined in the method of determining the fixation disclosed in JP-A No. 2013-96540. Moreover, the fixation can be determined only when the vehicle is stopped in the method of determining the fixation disclosed in JP-A No. 2013-96540.